Gas permeable contact lens and method and materials for its manufacture

ABSTRACT

A polymer is prepared by forming a mixture of 3-methacryloxypropytris(trimethylsiloxy) silane, methacrylic acid, cyclohexylmethacrylate, 2-hydroxypropylmethacrylate, m,p-styrylethyltrimethoxysilane, methyl methacrylate and a cross linker. A polymerization initiator is added to the mixture, and UV or thermal energy is supplied so that the mixture polymerizes to form a polymer that is transparent, hard, machinable and oxygen permeable. The polymer is cut into lenses, and the lenses are treated with acetyl chloride or another suitable chemical so that their surfaces become hydrophilic. The result is oxygen-permeable, hydrophilic, daily and extended-wear, hard contact lenses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to contact lenses and, more particularly, to anovel and highly-effective daily-wear and extended-wear contact lens andto a method and material for its manufacture.

2. Description of the Prior Art

There is a great need for a contact lens that can be worn safely,comfortably and continuously for an extended time, for example one ortwo months, and that is inexpensive enough to be discarded after thattime. It is essential that such a lens be highly oxygen permeable, sincethe pupil of the eye has no blood circulation and extracts the oxygenneeded by its cells directly from the atmosphere. Ideally, such a lensshould be hard so that it can correct for astigmatism. In order to becomfortable for the wearer, however, the lens must also be hydrophilic;that is, the contact angle of an air-water interface with a surface ofthe lens must be small.

In conventional practice, measures taken to increase oxygen permeabilityincrease contact angle, so that the lens becomes uncomfortable, andmeasures taken to reduce contact angle reduce oxygen permeability, sothat the lens cannot be worn continuously for an extended period. Thistrade-off has thus far defeated efforts to produce an extended-wearcontact lens having all of the desired properties.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to remedy the problems outlined above andin particular to provide a novel, oxygen-permeable, hydrophilic,extended-wear, hard contact lens and a method and easily-machinableinexpensive material for its manufacture.

In accordance with one aspect of the invention, a method of making aplastic material for a contact lens comprises the steps of:

forming a mixture comprising initiators and at least one polymerizablesilicone monomer selected from the group consisting of ##STR1## andmixtures thereof, where

R₁ is selected from the group consisting of ##STR2## where n=1 to 6, andmixtures thereof,

R₂ is selected from the group consisting of an alkyl group having from 1to 8 carbon atoms, a saturated cyclic group and a benzene ring, andmixtures thereof,

R₃ is selected from the group consisting of ##STR3## where n=1 to 6, andmixtures thereof, and

R₄ is selected from the group consisting of ##STR4## where n=1 to 6, andmixtures thereof; and

supplying energy to said mixture so that said mixture polymerizes toform a polymer that is transparent, hard, machinable and oxygenpermeable.

In accordance with a second aspect of the invention, a polymer formaking a contact lens comprises 0% to 30% by weight of a hydrophilicagent, 0.1% to 5% by weight of a cross linker, 0.05% to 1.0% by weightof a polymerization initiator, and 2% to 94.85% by weight of at leastone polymerizable silicone monomer selected from the group consisting of##STR5## and mixtures thereof, where

R₁ is selected from the group consisting of ##STR6## when n=1 to 6, andmixtures thereof,

R₂ is selected from the group consisting of an alkyl group having from 1to 8 carbon atoms, a saturated cyclic group and a benzene ring, andmixtures thereof,

R₃ is selected from the group consisting of ##STR7## where n=1 to 6, andmixtures thereof, and

R₄ is selected from the group consisting of ##STR8## where n=1 to 6, andmixtures thereof,

the polymer being transparent, hard, machinable and oxygen permeable.

In accordance with a third aspect of the invention, a contact lens ismade of a polymer comprising 0% to 30% by weight of a hydrophilic agent,0.1% to 5% by weight of a cross linker, 0.05% to 1.0% by weight of apolymerization initiator, and 2% to 94.5% by weight of a polymerizablesilicone monomer selected from the group consisting of ##STR9## andmixtures thereof, where

R₁ is selected from the group consisting of ##STR10## when n=1 to 6, andmixtures thereof,

R₂ is selected from the group consisting of an alkyl group having from 1to 8 carbon atoms, a saturated cyclic group and a benzene ring, andmixtures thereof,

R₃ is selected from the group consisting of ##STR11## where n=1 to 6,and mixtures thereof, and

R₄ is selected from the group consisting of ##STR12## where n=1 to 6,and mixtures thereof,

the lens being transparent, hard, machinable and oxygen permeable.

BRIEF DESCRIPTION OF THE DRAWING

A better understanding of the objects, features, and advantages of theinvention can be gained from the following description of the preferredembodiments thereof, in conjunction with the appended figures of thedrawings, wherein:

FIG. 1 is a plan view of a contact lens constructed in accordance withthe invention;

FIG. 2 is a sectional view taken along the line 2--2 of FIG. 1 andlooking in the direction of the arrows;

FIG. 3 is a sectional view in elevation illustrating apparatus formeasuring the contact angle of an air-water interface with a surface ofa contact lens; and

FIG. 4 is an enlarged view illustrating the contact angle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a contact lens 10 made in accordance with theinvention. The lens 10 comprises an inner surface 12 ("base curve") thatmakes contact with the eyeball of the wearer so that it covers at leastthe pupil and an outer surface 14 that is intermittently wiped orcovered by the eyelid. The lens 10 is curved to conform substantially tothe shape of the portion of the eyeball covered by the lens and may bethicker at the center than at the edges ("convex"), as shown, to improvevision at close distances or thicker at the edges than at the center("concave") to improve vision at long distances. If the lens is hard andformed with spherical surfaces, it automatically corrects forastigmatism as well as nearsightedness or farsightedness to the extentthat the astigmatism is due to nonspherical curvature of the front ofthe eyeball.

FIG. 3 shows apparatus 16 for measuring the contact angle of anair-water interface with a surface of a contact lens. In this case, thelens 10 is submerged in water (or preferably normal saline) 18 containedin a vessel 20, and an air bubble 22 is introduced by a syringe 24provided with a long, curved needle 26 so that the air bubble 22 istrapped below the lower surface 14 of the lens. It is also possible toplace a drop of water (or preferably normal saline) on a lens in air,and to measure the contact angle through the drop of water. The methodillustrated is preferred, however, since it measures the contact angleof the lens when the lens is hydrated and therefore more nearlyduplicates the conditions that prevail when the lens is in place in theeye.

In either case, an air-water interface 28 forms a contact angle A (FIG.4) with the lens surface. The contact angle A is measured through thewater or normal saline 18 and is defined by tangents T1 and T2 to theair bubble 22 and to the surface 14 of the lens, respectively. Thetangents T1 and T2 are taken at the intersection of the air bubble 22and the surface 14 of the lens. If the angle A is large, for example 60°or more, it indicates that the surface is relatively hydrophobic, likethe waxed finish of a car on which raindrops form into beads. A contactlens having a hydrophobic surface is uncomfortable for the wearer. Onthe other hand, if the contact angle A is small, for example 25° orless, it indicates that the surface is relatively hydrophilic. A contactlens having a hydrophilic surface is much more comfortable for thewearer.

In accordance with the invention, a plastic material for making acontact lens is prepared by forming a mixture comprising 0% to 30% byweight of a hydrophilic agent, 0.1% to 5% by weight of a cross linker,0.05% to 1.0% by weight of a polymerization initiator, and 2% to 94.85%by weight of at least one polymerizable silicone monomer selected fromthe group consisting of ##STR13## and mixtures thereof, where

R₁ is selected from the group consisting of ##STR14## when n=1 to 6, andmixtures thereof,

R₂ is selected from the group consisting of an alkyl group having from 1to 8 carbon atoms, a saturated cyclic group and a benzene ring, saidmixtures thereof,

R₃ is selected from the group consisting of ##STR15## where n=1 to 6,and mixtures thereof, and

R₄ is selected from the group consisting of ##STR16## where n=1 to 6,and mixtures thereof; and

supplying energy to the mixture so that the mixture polymerizes to forma polymer that is transparent, hard, machinable and oxygen permeable.

Energy is supplied to the mixture so that the mixture polymerizes toform a polymer that is transparent, hard, machinable and oxygenpermeable. The polymerization temperature is within a range of 30° C. to70° C. The time for polymerization to be completed using heat energyranges from 48 hours (at 30° C.) for 30 minutes (at 70° C.).Polymerization may be completed at room temperature in 30 minutes to onehour using ultraviolet radiation.

The polymerizable material is preferably m,p-styrylethyltrimethoxysilaneor S1588, and the cross linker is preferablyethyleneglycoldimethacrylate or EGDMA.

The polymerization initiator is selected from the group consistingessentially of 2,2'-azobis(2,4-dimethylvaleronitrile) or VAZ052,benzoinmethylether or BME, and sec-butylperoxydicarbonate or SBC. Thefirst initiator may be used when polymerization is aided by ultravioletor thermal radiation, the second when polymerization is aided byultraviolet radiation, and the third when polymerization is aided bythermal radiation. The polymerization initiator is present in themixture in an amount ranging from 0.05% to 0.5% by weight.

Energy is supplied in the form of thermal energy or in the form ofultraviolet radiation, as may be appropriate in view of the initiatoremployed.

Preferably the mixture comprising substantially 50% by weight of3-methacryloxypropytris(trimethylsiloxy)silane or OTC1, substantially 8%by weight of methacrylic acid or MA, substantially 7% by weight ofcyclohexylmethacrylate or CHMA, substantially 5% by weight of2-hydroxypropylmethacrylate or 2-HPMA, substantially 15% by weight ofm,p-styrylethyltrimethoxysilane or S1588, substantially 14% by weight ofmethyl methacrylate or MMA, and substantially 1% by weight ofethyleneglycoldimethacrylate or EGDMA.

The method further comprises the steps of forming the polymer into acontact lens and treating a surface of the contact lens with a chemicalto reduce the contact angle of an air-water interface with the surfaceof the lens. The chemical is preferably selected from the groupconsisting essentially of NaOH, AcCl, and H₂ SO₄.

Thus the polymer for making the contact lens comprises the sameconstituents in the same proportions as the mixture described above. Theresulting lens also comprises the same materials in the sameproportions.

Before the treatment to hydrophilize the surfaces of the lens, thepolymer in one embodiment of the invention (employing S1588) may berepresented as ##STR17## where R is ##STR18##

Treatment with 5% by weight H₂ SO₄ in 95% by weight of H₂ O for one houryields a mixture of ##STR19## on the surfaces of the contact lens andevolves CH₄ as a gas. The resulting lens has a shore hardness (D scale)within the range of 80 to 90. Oxygen permeability in ml cm/cm² seccmHg×10⁻¹⁰ is shown in the second two columns of Table I (normal eyetemperature to about 35° C.).

                  TABLE I                                                         ______________________________________                                        lens center                                                                   thickness (mm)   25° C.                                                                         35° C.                                        ______________________________________                                        .125             40.9    51.8                                                 .157             43.5    57.7                                                 .215             45.0    60.2                                                 .295             47.1    64.4                                                 ______________________________________                                    

Contact angle is shown in Table 2.

                  TABLE II                                                        ______________________________________                                                         After surface treat-                                                                         After surface                                 Before In        ment with 2N NaOH                                                                            treatment with                                surface                                                                              saline    for 20 minutes and                                                                           25% AcCl for                                  treatment                                                                            for 48 hrs                                                                              saline for 48 hrs                                                                            20 minutes                                    ______________________________________                                        31°-60°                                                                11°-65°                                                                   12°-25°                                                                        15°                                    ______________________________________                                    

Light transmission is 97+%, specific gravity is about 1.09, andrefractive index is about 1.47.

Before the treatment to hydrophilize the surfaces of the lens, thepolymer in another embodiment of the invention (employing T3633) may berepresented as ##STR20## where R' is ##STR21##

Treatment with 5% by weight H₂ SO₄ in 95% by weight of H₂ O for one houryields: ##STR22## on the surfaces of the contact lens and evolves CH₄ asa gas. The resulting lens has a shore hardness (D scale) within therange of 80 to 90. Oxygen permeability and contact angle are close tothe values set forth in Tables I and II for lenses made from a polymeremploying S1588. Light transmission is 97+%, specific gravity about1.09, and refractive index is about 1.47. The material is however morebrittle than that made with S1588.

EXAMPLE I

The following are mixed at 70° C. in a 100 ml beaker:

    ______________________________________                                        3-methacyloxypropytris(trimethylsiloxy)                                                                5.0 grams                                            silane or OTCl                                                                methacrylic acid or MA   .8 grams                                             cyclohexylmethacrylate or CHMA                                                                         .7 grams                                             2-hydroxypropylmethacrylate or 2-HPMA                                                                  .5 grams                                             m,p-styrylethyltrimethoxysilane or S1588                                                               1.5 grams                                            methyl methacrylate or MMA                                                                             1.4 grams                                            ethyleneglycoldimethacrylate or EGDMA                                                                  .1 grams                                             ______________________________________                                    

The ethyleneglycoldimethacrylate or EGDMA serves as a cross linker. Asan initiator 0.02 grams of 2,2'-azobis(2,4-dimethylvaleronitrile) orVAZ052 is added to the mixture, and the mixture while at roomtemperature is subjected to ultraviolet radiation from a 20-wattultraviolet lamp placed at a distance of approximately 20 cm from themixture. The mixture polymerizes within 30 minutes to form a hardpolymer. The polymer is easily cut to the shape of a contact lens havinga center thickness of 0.2 mm or less and polished. The lens is highlytransparent and has uniform optical properties. It has an oxygenpermeability of 58.6×10⁻¹⁰ ml cm/cm² sec cmHg at 35° C. The lens issubjected to a surface treatment with 25% AcCl for 20 minutes and isfound to have a contact angle of 8°.

The following examples are similar to Example I but illustratevariations of the materials and the quantities thereof employed.

EXAMPLE II

    ______________________________________                                        OTCl                   32     grams                                           MA                     4      grams                                           2-HPMA                 2.6    grams                                           T-3633                 10     grams                                           EDGMA                  1.42   grams                                           azobisisobutyronitrile or AIBN                                                                       0.3    grams                                           ______________________________________                                    

EXAMPLE III

    ______________________________________                                               OTCl   3.08 grams                                                             MA     0.39 grams                                                             CHMA   0.34 grams                                                             2-HPMA 0.24 grams                                                             S-1588 1.00 grams                                                             AIBN   0.03 grams                                                      ______________________________________                                    

EXAMPLE IV

    ______________________________________                                               OTCl         2.9    grams                                                     MA           0.4    grams                                                     CHMA         0.35   grams                                                     2-HPMA       0.25   grams                                                     S-1588       0.53   grams                                                     T-3633       0.51   grams                                                     EGDMA        0.10   grams                                                     AIBN         0.03   grams                                              ______________________________________                                    

EXAMPLE V

    ______________________________________                                               OTCl         2.9    grams                                                     MA           0.4    grams                                                     CHMA         0.35   grams                                                     2-HPMA       0.25   grams                                                     S-1588       0.25   grams                                                     T-3633       0.75   grams                                                     EGDMA        0.10   grams                                                     AIBN         0.03   grams                                              ______________________________________                                    

EXAMPLE VI

    ______________________________________                                               OTCl         2.5    grams                                                     MA           0.4    grams                                                     2-HPMA       0.25   grams                                                     MMA          0.75   grams                                                     S-1588       0.26   grams                                                     T-3633       0.75   grams                                                     EGDMA        0.10   grams                                                     AIBN         0.03   grams                                              ______________________________________                                                CL EXAMPLE VII

    ______________________________________                                               OTCl         2.5    grams                                                     MA           0.39   grams                                                     CHMA         0.35   grams                                                     2-HPMA       0.25   grams                                                     MMA          0.70   grams                                                     S-1588       0.75   grams                                                     EGDMA        0.05   grams                                                     AIBN         0.03   grams                                              ______________________________________                                    

EXAMPLE VIII

    ______________________________________                                        OTC1              2.50 grams                                                  MA                0.40 grams                                                  CHMA              0.35 grams                                                  Isoborylmethacrylate                                                                            0.70 grams                                                  S-1588            0.75 grams                                                  EGDMA             0.05 grams                                                  2-HPMA            0.25 grams                                                  AIBN              0.03 grams                                                  ______________________________________                                    

Thus there is provided in accordance with the invention a novel,disposable, extended-wear, oxygen-permeable, hydrophilic, inexpensive,hard contact lens and a method and easily machinable material for itsmanufacture. Many modifications of the preferred embodiments of theinvention disclosed above will readily occur to those skilled in the artupon consideration of this disclosure. For example, initiators andsurface-treatment chemicals other than the ones disclosed may beemployed, the contact lens may be tinted or clear, the temperatures andtimes of polymerization may vary, etc. Accordingly, the invention is notlimited except by the appended claims.

I claim:
 1. A contact lens made of a polymer comprising 0% to 30% byweight of a hydrophilic agent, 0.1% to 5% by weight of a cross linker,0.05% to 1.0% by weight of a polymerization initiator, and 2% to 94.85%by weight of a polymerizable silicone monomer selected from the groupconsisting of ##STR23## and mixtures thereof, where R₁ is selected fromthe group consisting of ##STR24## where n=1 to 6, and mixtures thereof,R₂ is selected from the group consisting of an alkyl group having from 1to 8 carbon atoms, a saturated cyclic group and a benzene ring, andmixtures thereof,R₃ is selected from the group consisting of ##STR25##where n=1 to 6, and mixtures thereof, and R₄ is selected from the groupconsisting of ##STR26## where n=1 to 6, and mixtures thereof, and saidlens being transparent, hard, machinable and oxygen permeable.
 2. Acontact lens according to claim 1 wherein said polymerization siliconemonomer is p-styrylethyltrimethoxysilane.
 3. A contact lens according toclaim 1 wherein said cross linker is selected from the group consistingof ethyleneglycoldimethacrylate, diethyleneglycoldimethacrylate,triethyleneglycoldimethacrylate, tetraethyleneglycoldimethacrylate,silicone containing cross linkers, and mixtures thereof.
 4. A contactlens according to claim 1 having a surface that is hydrophilic to such adegree that the contact angle of an air-water interface with saidsurface is less than 25 degrees.
 5. A contact lens according to claim 3wherein said angle is substantially 8 degrees.